Carbon fiber reinforced plastic materials (CFRPs) have utility in structures including, without limitation, vehicles including, without limitation, aircraft. CFRPs comprise a fiber material (e.g. carbon fibers, etc.) impregnated with a resin material (e.g. epoxy resin, acrylic resin, etc.) to make so-called prepregs. Prepregs are partially cured layers that can be manufactured into rolls that can yield unrolled sheets for use in composite material manufacture. Prepreg material, or “prepregs” can then be “laid-up” or “stacked” into multi-layered “stacks” that can be shaped on forming mandrels or other tooling, followed by curing or partially curing the shaped material to produce a composite material that, if desired, adopts desired and predetermined shapes and dimensions imparted by the tool, with the composite material having desired weight and strength. Alternately, prepregs may be oriented into a stack that is trimmed and cured to form a solid stack for use as a composite material structure or other type of composite component.
CRFPs can be used as structural components in aircraft (e.g. stringers, spars, ribs, etc.). Over time, a composite material, such as those comprising CFRPs, may experience fissures or cracks, requiring repair or replacement. Such repair or replacement is time-consuming and costly as the larger structure comprising the composite material must be taken out of service. Attempts to protect components comprising CFRPs and other composite materials can include an overwrap, or other layer, for example, a cured fabric layer, to afford a compressive force to, and otherwise reinforce and protect the composite material. However, at times, protective overwrap materials, such as, for example, curable fabric material shells, etc., may possess characteristics that can contribute to the degradation of the underlying composite material. For example, if an overwrap shell material has a different coefficient of thermal expansion (CTE), and/or a different Young's modulus as compared with the CTE and modulus of the composite material the overwrap material may not afford the composite material adequate protection from damage or degradation, and may contribute to such degradation. For the purpose of the present disclosure, the term “modulus” is used equivalently and is therefore interchangeable with the term “Young's modulus”, unless explicitly stated otherwise.
A mismatch in the CTE and/or modulus of the composite stack and the shell material overwrapping the composite stack can cause damage to the composite stack of the stacked-up prepreg ply assembly (e.g. the composite material “stack”) shrinks or expands to a greater extent as compared to the overwrap shell. As a result, curing and “wrapping” stages during manufacture of the composite component, as well as conditions experienced by the wrapped composite material in use, may result in thermo-stress and cause fissures, cracks, and/or micro-cracks at the edges of the composite material stack. Such cracks often initiate at the composite material edge. If detected upon component inspection, such composite material damage results in the rejection of such a composite component or part, creating material waste and increased manufacturing cost. If damage occurs to a composite component that has been installed in a larger structure and is “in service”, repair or replacement of the damaged composite part may be required, also resulting in material waste, and increased cost while the larger structure comprising the composite component is taken out of service for repair.
Further, composite components made from composite materials may be used in the manufacture of larger structures (e.g. aircraft). Such structures may encounter electromagnetic effects (EMEs) including, for example, and without limitation, lightning strikes. When a structure encounters an EME, the charge delivered to the structure travels throughout any conductive path, and can cause damage to exposed dielectric materials, including composite materials. The electrical damage to composite materials from EMEs can be exacerbated if the edges of the composite material comprise exposed carbon fibers.